Patterned Optical Structures With Enhanced Security Feature

ABSTRACT

A security article is a substrate having a diffractive grating thereon, coated with a windowed high index layer and a color shifting coating visible through the window. The color shifting coating is disposed on the high index layer or on the opposite side of the substrate. Alternatively, a thin film color shifting structure conforming the diffractive grating is disposed between the grating and the windowed high index layer, also conforming to the shape of the diffractive grating. Alternatively, an ink with low density of color shifting pigments is applied over the high index layer conforming to the shape of the diffractive grating. The resulting color shifting image provides a reference to a holographic image.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. patent application Ser. No.60/827,487 filed Sep. 29, 2006, which is hereby incorporated in itsentirety for all purposes.

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 11/552,219 filed Oct. 24, 2006, which claimspriority from provisional application No. 60/759,350 filed Jan. 17, 2006and provisional application No. 60/729,907 filed Oct. 25, 2005, thedisclosures of which are hereby incorporated in their entirety for allpurposes.

The application Ser. No. 11/552,219 is a continuation-in-partapplication of patent application Ser. No. 11/273,985 filed Nov. 15,2005, which is a continuation-in-part application of patent applicationSer. No. 10/666,318 filed on Sep. 18, 2003, issued as U.S. Pat. No.6,987,590; and claims priority from provisional patent application Ser.No. 60/673,080 filed Apr. 20, 2005; the disclosures of which are herebyincorporated in their entirety for all purposes.

The application Ser. No. 11/552,219 is a continuation-in-partapplication of patent application Ser. No. 11/313,165 filed Dec. 20,2005, which is a continuation-in-part application of patent applicationSer. No. 11/022,106, filed Dec. 22, 2004, which is acontinuation-in-part application of patent application Ser. No.10/386,894 filed Mar. 11, 2003, now issued as U.S. Pat. No. 7,047,883,which claims priority from U.S. Provisional Patent Application Ser. No.60/410,546 filed Sep. 13, 2002, from U.S. Provisional Patent ApplicationSer. No. 60/410,547 filed Sep. 13, 2002; and from U.S. ProvisionalPatent Application Ser. No. 60/396,210 filed Jul. 15, 2002, thedisclosures of which are hereby incorporated in their entirety for allpurposes.

The application Ser. No. 11/552,219 is a continuation-in-partapplication of patent application Ser. No. 10/706,142 filed Nov. 12,2003, which is a divisional application of patent application Ser. No.09/351,102 filed Jul. 8, 1999, now issued as U.S. Pat. No. 6,761,959,the disclosures of which are hereby incorporated in their entirety forall purposes.

The application Ser. No. 11/552,219 is a continuation-in-partapplication of patent application Ser. No. 11/047,389 filed Jan. 31,2005, now issued as U.S. Pat. No. 7,224,528, which is a continuationapplication of patent application Ser. No. 10/705,610 filed Nov. 10,2003, which is a divisional application of patent application Ser. No.09/489,250 filed Jan. 21, 2000, the disclosures of which are herebyincorporated in their entirety for all purposes.

THE FIELD OF THE INVENTION

The present invention is related generally to thin film optical coatingsfor use in producing security articles. More specifically, thisinvention is related to the production of diffractive surfaces such asholograms or gratings coated with a material having a high refractiveindex, which can be used as security articles in a variety ofapplications.

BACKGROUND OF THE INVENTION

Color-shifting pigments and colorants have been used in numerousapplications, ranging from automobile paints to anti-counterfeiting inksfor security documents and currency. Such pigments and colorants exhibitthe property of changing hue upon variation of the angle of incidentlight, or as the viewing angle of the observer is shifted. The primarymethod used to achieve such color-shifting colorants is to dispersesmall flakes, which are typically composed of multiple layers of thinfilms having particular optical characteristics, throughout a mediumsuch as paint or ink that may then be subsequently applied to thesurface of an object. Color switching pigments appear to change colorfor example from a dark green to a light green, or from a light blue toa dark blue. Color switching pigments are described in U.S. Pat. No.6,150,022 in the name of Coulter et al. Color switching pigments consistof bright metal flakes that are substantially reflective disposed in aliquid carrier vehicle that includes a dye. For example when a bluecarrier vehicle is used, the flakes have a range of color from light todark blue when they switch color upon a change in viewing angle.

Diffraction patterns and embossments, and the related field ofholographs, have begun to find wide-ranging practical applications dueto their aesthetic and utilitarian visual effects. For all intents andpurposes, a diffraction pattern, whether embossed, etched or inked, isunderstood to be a marked region. A marked region is to be understood tobe a region having some form of indicia thereon, whether inked orstamped or etched. One very desirable decorative effect is theiridescent visual effect created by a diffraction grating. This strikingvisual effect occurs when ambient light is diffracted into its colorcomponents by reflection from the diffraction grating. In general,diffraction gratings are essentially repetitive structures made of linesor grooves in a material to form a peak and trough structure. Desiredoptical effects within the visible spectrum occur when diffractiongratings have regularly spaced grooves in the range of hundreds tothousands of lines per millimeter on a reflective surface.

Diffraction grating technology has been employed in the formation oftwo-dimensional holographic patterns which create the illusion of athree-dimensional image to an observer. Three-dimensional holograms havealso been developed based on differences in refractive indices in apolymer using crossed laser beams, including one reference beam and oneobject beam. Such holograms are called volume holograms or 3D holograms.Furthermore, the use of holographic images on various objects todiscourage counterfeiting has found widespread application.

There currently exist several applications for surfaces embossed withholographic patterns which range from decorative packaging such as giftwrap, to security documents such as bank notes and credit cards.Two-dimensional holograms typically utilize diffraction patterns whichhave been formed on a plastic surface. In some cases, a holographicimage which has been embossed on such a surface can be visible withoutfurther processing; however, it is generally necessary to coat areflective layer upon the embossed surface, typically a thin metal layersuch as aluminum in order to achieve maximum optical effects. Thereflective layer substantially increases the visibility of thediffraction pattern embossment.

Every type of first order diffraction structure, including conventionalholograms and grating images, has a major shortcoming even ifencapsulated in a rigid plastic. When diffuse light sources, such asordinary room lights or an overcast sky, are used to illuminate theholographic image, all diffraction orders expand and overlap so that thediffraction colors are lost and not much of the visual informationcontained in the hologram is revealed. What is typically seen is only asilver colored reflection from the embossed surface and all such deviceslook silvery or pastel, at best, under such viewing conditions. Thus,holographic images generally require direct specular illumination inorder to be visualized. This means that for best viewing results, theilluminating light must be incident at the same angle as the viewingangle.

Since the use of security holograms has found widespread application,there exists a substantial incentive for counterfeiters to reproduceholograms which are frequently used in credit cards, banknotes, and thelike. Thus, a hurdle that security holograms must overcome to be trulysecure, is the ease at which such holograms can be counterfeited. Onestep and two step optical copying, direct mechanical copying and evenre-origination have been extensively discussed over the Internet.Various ways to counteract these methods have been explored but none ofthe countermeasures, taken alone, has been found to be an effectivedeterrent.

One method used to reproduce holograms is to scan a laser beam acrossthe embossed surface and optically record the reflected beam on a layerof a material such as a photopolymerizable polymer. The original patterncan subsequently be reproduced as a counterfeit. Another method is toremove the protective covering material from the embossed metal surfaceby ion etching, and then when the embossed metal surface is exposed, alayer of metal such as silver (or any other easily releasable layer) canbe deposited. This is followed by deposition of a layer of nickel, whichis subsequently released to form a counterfeiting embossing shim.

Due to the level of sophistication of counterfeiting methods, it hasbecome necessary to develop more advanced security measures. Oneapproach, disclosed in U.S. Pat. Nos. 5,624,076 and 5,672,410 to Miekkaet al., where embossed metal particles or optical stack flakes are usedto produce a holographic image pattern.

A further problem with security holograms is that it is difficult formost people to identify and recollect the respective images produced bysuch holograms for verification purposes. The ability of the averageperson to authenticate a security hologram conclusively is compromisedby the complexity of its features and by confusion with decorativediffractive packaging. Thus, most people tend to confirm the presence ofsuch a security device rather than verifying the actual image. Thisprovides the opportunity for the use of poor counterfeits or thesubstitution of commercial holograms for the genuine security hologram.

In other efforts to thwart counterfeiters, the hologram industry hasresorted to using more complex images such as producing multiple imagesas the security device is rotated. These enhanced images provide theobserver with a high level of “flash” or aesthetic appeal.Unfortunately, this added complexity does not confer added securitybecause this complex imagery is hard to communicate and recollection ofsuch imagery is difficult, if not impossible, to remember.

It would therefore be of substantial advantage to develop improvedsecurity products which provide enhanced viewing qualities in variouslighting conditions, especially in diffuse lighting, and which areusable in various security applications to make counterfeiting moredifficult.

Security articles having diffractive surfaces and color-shiftingbackgrounds are described U.S. patent application Ser. Nos. 20040105963A1, 20040101676 A1, 20040094850 A1, and 20040081807 A1. Such securitydevices include a transparent holographic substrate coated with acolor-shifting layer on the side opposite to the holographic embossing.The color-shifting optical coating provides an observable color shift asthe angle of incident light, or viewing angle, changes. Thecolor-shifting coating can be fabricated by vacuum deposition of anoptical interference structure onto the corresponding surface of thesubstrate, by spraying of a paint containing color-shifting pigment, orby printing ink as by flexographic, gravure or Intaglio means.

A patterned layer of a reflective material might be applied overpredetermined portions of the holographic substrate to form alphanumericcharacters, bar codes, pictorial or graphic designs as described in WO2005/026848 A2. To produce such, a highly reflective material needs tobe deposited on the top of the holographic substrate and etched out frompredetermined portions of the substrate. As a result of demetalizingthese areas of the substrate, where the metal was etched out, theybecome essentially transparent and the holographic effect there becomesalmost invisible. In contrast, the portions of the substrate where thereflective metal was left on the surface in different predeterminedshapes, maintain visible holographic properties.

Color-shifting coatings can be applied to such a demetalized structurein different ways. It can be applied to the side of the substrateopposite to the embossed side. In this manner the coating becomesvisible through transparent demetalized portions of the substrate.Alternatively the color-shifting coating can be applied on the top ofembossed side. The coating and patterned holographic elements becomevisible through the transparent substrate when the substrate is flippedover. This combination of hologram substrate and a color-shiftingcoating is called a “chromagram”. General concept of chromagrams can bereadily understood with reference to FIGS. 1 through 5.

Demetalized holograms are more difficult to counterfeit since one notonly has to make the hologram but also demetalize an intricate patternin register with the holographic pattern.

It is an object of this invention, to provide an image that can be usedas a security device, that is very difficult for counterfeiters to copy,and that can readily be authenticated.

It is a further object of the invention to provide a security devicethat offers a high degree of security while at same time providingconsiderable visual appeal.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a security devicehaving a first region coated with magnetically aligned pigmentparticles; and, a second marked region different from the first printedregion, wherein the magnetically aligned pigment forms an image thatappears to move with a change in viewing angle or incident light, andwherein the second marked region serves as a frame of reference againstwhich the image appears to move.

In accordance with the invention, there is further provided a securitydevice having a first region coated with a magnetically aligned pigmentand a second different region having a diffraction grating thereon,wherein the magnetically aligned pigment forms an image that appears tomove with a change in viewing angle or angle of incident light, andwherein the diffraction grating serves as a frame of reference againstwhich the image appears to move.

In accordance with the invention, there is provided a security devicecomprising a patterned reflective optical structure having: a substratehaving a diffraction grating therein or thereon; an at least partiallyreflective layer adjacent to or near the diffraction grating; and, alayer of field aligned pigment supported by the substrate.

In accordance with the invention, there is provided a security devicecomprising a substrate having a diffraction grating therein or thereon;a segmented high refractive index (HRI) layer adjacent to or near thediffraction grating; and an optically variable coating visible inwindows of the HRI layer. The OV coating can be a color-shifting layeredstructure, or a carrier having color-shifting or reflective pigments orflakes therein.

In accordance with the invention, there is provided a security devicehaving a first region coated with a magnetically aligned pigment and asecond different region having a diffraction grating thereon, whereinthe magnetically aligned pigment forms an image that appears to movewith a change in viewing angle or angle of incident light, and whereinthe diffraction grating serves as a frame of reference against which theimage appears to move, wherein the first region is contained withinboundaries of the second region, or, wherein the second region iscontained within boundaries of the first region, and wherein both thediffraction grating and the magnetically aligned pigment can be seenfrom one side of the device.

In accordance with the invention, there is provided a security devicecomprising a substrate having a surface that is partially embossed suchthat embossed regions on said surface are separated by non-embossedregions forming windows and a layer of magnetically aligned pigmentabove, below or within the windows and visible through the windows,whereby diffractive effects are seen from the embossed regions separatefrom effects seen from the magnetically aligned pigment seen through orin the windows when the device is irradiated with light.

In accordance with the invention, there is provided a security devicethat includes a layer having a diffractive region and a different layerhaving a magnetically aligned pigment, wherein when the device isirradiated with light, diffractive and kinematic effects are seen.

In accordance with a broad aspect of the invention, there is provided asecurity device comprising a layer having a diffraction pattern thereinor thereon, and another layer formed of a color-shifting coating whereinonly some regions of the color-shifting coating are magneticallyaligned.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described inconjunction with the drawings in which:

FIG. 1 is a security image formed in accordance with the prior art,wherein a polyester substrate is embossed with a pattern and whereinparticular areas are metalized.

FIG. 2 is a cross section of the image of FIG. 1.

FIG. 3 is a cross section of a security image similar to FIG. 1 whereinan additional layer of color-shifting pigment has been deposited on theunderside of the substrate.

FIG. 4 a is a plan view of the image of FIG. 3 having a diffractiongrating and color-shifting coating under the grating.

FIG. 4 b is a cross sectional view of a structure wherein the grating orhologram is embossed on the underside of the substrate and wherein acolor-shifting coating is directly next to the embossing.

FIG. 5 is a plan view of the chroma shown in FIG. 4 b.

FIG. 6 a is a plan view of an embodiment of the invention wherein acolor-shifting magnetically aligned layer is adjacent to the hologram ordiffraction grating yielding a chromagram that has optically-illusivecolor-shifting effects from the magnetically aligned color-shiftingpigment and diffractive effects from the hologram.

FIG. 6 b is a view of the embodiment shown in FIG. 6 a whereby planesthrough sections 11 and 12 taken in FIG. 6 a are shown.

FIG. 7 a is a detailed cross-section of the chromagram shown in FIG. 6 ataken along line 11 in the plane shown if FIG. 6 b.

FIG. 7 b is a detailed cross-section of the chromagram shown in FIG. 6 ataken along line 12 in the plane through line 12 shown if FIG. 6 b.

FIG. 8 is a plan view of a magnetic print and the graphical design for asecurity thread used on banknotes.

FIG. 9 is a more detailed view of a portion of FIG. 8.

FIG. 10 is a cross-section as shown in FIGS. 8 and 9 wherein the threadwas flipped over after curing of the ink and laminated with adhesive tothe paper.

FIG. 11 is a cross-sectional view of an alternative embodiment whereinthe aligned color-shifting coating is deposited on an opposite side ofthe substrate from the segmented diffraction grating.

FIG. 12 is a cross-sectional view of an alternative embodiment whereinthe color-shifting coating 8 is applied to a non-embossed side on thesubstrate and placed into a field to align magnetic particles to formthe 100 pattern; and after curing of the ink the structure is laminatedto a paper with adhesive.

FIG. 13 is a demetalized holographic embossing overlap the magneticallyformed image to enhance its appearance having an aluminum metalizedembossed frame and metalized embossed contours in the shape of theletters AB.

FIG. 14 is a cross-section of the substrate of FIG. 13.

FIG. 15 is an image in accordance with an embodiment of the inventionwherein color-shifting magnetically aligned flakes are disposed under ahologram.

FIG. 16 is a cross-sectional view of the image of FIG. 15.

FIG. 17 is the cross-sectional view of the image of FIG. 15 shown tiltedat a different angle than FIG. 16.

FIG. 18 is the image shown in FIG. 17.

FIG. 19 a is an image in accordance with an embodiment of this inventionwherein a bridge is shown having water thereunder, wherein the waterappears to move relative to the bridge as the image is tilted.

FIGS. 19 b through 19 d are figures of different magnetic arrangementsthat can be used to produce magnetic fields that can arrange themagnetically alignable pigment so that it appears is if the water ismoving upon tilting the image of FIG. 19 a.

FIG. 19 e is a view of the image in FIG. 19 a prior to adding thecolor-shifting magnetic pigment and aligning the flakes in a magneticfield.

FIG. 19 f is a view of the image in FIG. 19 e with magnetic ink added inthe field under the bridge.

FIGS. 20 b through 20 d are perspective views of the magneticarrangements shown in FIGS. 19 b through 19 d respectively.

FIG. 21 a is a cross-section of a chromagram having a color shiftingcoating on the side of the substrate opposite to the diffractive patterncoated with a windowed or segmented HRI layer.

FIG. 21 b is a cross-section of a chromagram having a color shiftingcoating on the windowed HRI layer.

FIG. 21 c is a cross-section of a chromagram wherein a color shiftingcoating is interposed between a diffractive grating and an HRI coating.

DETAILED DESCRIPTION

Referring now to FIG. 1 an image is shown having an embossed pattern. Apolyester substrate 1 is shown to have several different regionsdefining specific features in the image. Region 2 is embossed anddemetalized. This can readily be seen in FIG. 2. Regions 3 and 4 areembossed and metalized with a highly reflective coating of aluminum. Thecircle 5 and the star 6 were metalized with aluminum but not embossed.Region 7 shown in FIG. 1 was not embossed or metalized. The frame 8 wasmetalized but non-embossed. The fine lines 2 in the pattern of FIG. 1were barely visible because they were not coated with a reflectivemetal. The star 6 and the circle 5 exhibit a silver-like appearance. Thepatterns in regions 3 and 4 have a rainbow colored appearance because ofthe diffractive nature of the light reflected from embossings on theirsurfaces.

FIG. 3 illustrates an improvement over the structure shown in FIG. 2wherein a color-shifting coating 9 can be applied to the hologram shownin FIG. 1. The color-shifting coating 9 can be applied in two differentways, resulting in two different chromagrams. It can be applied to thesurface of the holographic substrate that is opposite to the embossedside as shown in FIG. 3. In this instance, the chromagram has anappearance as shown in FIG. 4 a. The difference of this chromagram withthe hologram in FIG. 1 is that the region 7 in FIGS. 3 and 4 a has acolor-shifting appearance.

According to another embodiment, the color-shifting coating 9 can beapplied on the top of embossing as shown in FIG. 4 b. To view the effectthe coated substrate needs to be flipped over as shown. In this instancethe embossing 2 disappears because the refraction indices of thetransparent substrate and the ink vehicle closely match one another. Thechromagram has an appearance shown in FIG. 5.

The images shown in FIGS. 4 a and 5 pictorially illustrate the conceptof the “chromagrams” as an optical structure, for example a hologram orgrating with a patterned demetalized layer of a reflective materialapplied over certain regions of the structure and an active opticalcoating applied over the patterned layer of reflective material andexposed portions of the surface of the structure.

In accordance with this invention, it is proposed to use a novel andinventive structure to form chromagrams for preventing of counterfeitsof valuable documents, credit cards, banknotes, and the like.

In accordance with an aspect of the invention, it is possible to enhancethe security properties of a patterned holographic structure by printinga color-shifting magnetically alignable optically visible coating or anon-color-shifting magnetically alignable optically visible coating andapplying a magnetic field thereto to form in this layer either threedimensional patterns or three dimensional informative signs or patternswith illusive optical effects. The coating should be based on an inkcontaining platelet-like magnetic pigments for example as described U.S.Pat. No. 6,808,806, or in co-pending U.S. patent applications Ser. Nos.20040051297, 20040166308, 20050123755, and 20060194040, incorporatedherein by reference for all purposes. The term “magnetic pigment” isused to mean a pigment that will align in a magnetic field. E-fieldalignable pigments may be used in place of magnetic pigments when anelectric field is used to align the pigment. Field alignable pigmentsare pigments that have flakes that will align in a magnetic or electricfield. Of course permanent magnets or electromagnets can be used togenerate magnetic fields. In accordance with this invention, themagnetic pigment can be color-shifting or non-color-shifting. The inkvehicle can be clear or dyed. To make a structure with the enhancedsecurity properties, the ink needs to be printed on the surface of thesubstrate as it was done for the above mentioned described chromagrams.The substrate with a layer of wet ink is moved into a magnetic field toform the illusory image. Preferably, the field is shaped to a desired,desirable, or predetermined pattern. When the wet ink is exposed to amagnetic or electric field, flat magnetic or e-field alignable particlesof the pigment align along magnetic lines of the field. This is shown inFIGS. 6 a, 6 b and 7 b.

FIG. 6 b more clearly illustrates an extended view whereby the planesalong where the cross-section is taken can be viewed.

Turning now to FIG. 6 a an image is shown having two section lines 11and 12 indicating cross-sections taken along lines 11-11 and 12-12. Thecross sectional drawing taken along line 11 is shown in FIG. 7 a, andthe cross-sectional drawing taken along line 12 is shown in FIG. 7 b.

UV or e-beam or thermal curing of the ink vehicle directly within thefield or shortly after its exposure to the field fixes magneticparticles inside of the layer of the ink at their aligned positions.When the ink is illuminated by the light source and observed with anaked eye or with an optical instrument the differently alignedplatelet-like shaped magnetic pigment particles reflect incident lightdifferently. One portion of the particles is so oriented with respect tothe substrate, to the light source and to the observer that it reflectscoming light rays right into the eye of the observer. Another portion ofthe particles of the print reflects light rays in different directionsbecause they are tilted at different angles relative to the direction ofthe observer. When the substrate with printed coating is tilted withrespect to the light source or the observer the first portion of thepigment particles does not reflect the light toward the observer anymore. These particles start to reflect the light in different directionwhile the particles of the second portion start to reflect the lightrays in the direction of the observer. When particles are alignedgradually in the layer of the ink, tilting of the substrate causesappearance of an illusive motion effect. When particles are alignedalong the lines of a magnet that was shaped in predetermined pattern aportion of the printed layer repeats the shape of the magnet creating aneffect of three-dimensionality. In this region it appears as if theimage comes out of the substrate toward the observer.

FIG. 6 a shows a chromagram fabricated according to the proceduredescribed in FIGS. 4 and 5. The color-shifting coating 9 in this figurewas fabricated by printing of a color-shifting magnetic ink on thesurface of a partially demetalized hologram 3. After the printing wascompleted the hologram with wet ink was placed in the magnetic field ofa star shaped magnet and subsequently cured with UV light. When viewedin the direction of the arrow as shown in FIG. 7 a, the chromagram showspresence of the star 10 that has virtual height close to 0.25″.

The chromagram with the enhanced security feature has a magneticallyprinted star around the star in hologram 2. It is generally importantthat the magnetically introduced pattern of the print was a part of thegraphical design of the security article.

The magnetically formed image can be placed inside of a holographicimage. An example of such combination of a magnetic print and thegraphical design for a security thread of banknotes is illustrated inFIGS. 8, 9, and 10 and 9. In FIG. 10 a polyester substrate 81 which ispartially aluminized has a layer of magnetically aligned flakesthereunder as shown.

The security thread 81 is attached to the paper substrate 82 bytraditional technology. The thread 81 is made from a thin transparentpolyester substrate, embossed in certain regions 83 with a shape of arectangular frame 84 and the number 100 inside of the frame 84. Both theframe 84 and the 100 in the region 83 are embossed with diffractivegrooves 85 using known technology for forming holograms.

Due to the embossing, a rainbow-colored diffractive pattern of the framewith the number 100 in the area 83 results. The embossed side of thesubstrate was coated with a thin aluminum layer 86. Part of aluminum wasetched off the substrate leaving rectangular windows 87 of the same sizeas the frames 84 of embossed boxes in the area 83. Color-shifting ink 88was applied to the embossed and partially aluminum-coated side of thesubstrate 82. The substrate with the wet ink 88 was placed in themagnetic field providing alignment of magnetic particles in the shape 89of the number 100 with the same size as the size of 100 in theholographic part of the thread. The magnetically formed number 100 has athree-dimensional like appearance. The thread was flipped over aftercuring of the ink and laminated with adhesive 90 to the paper 82 withthe color-shifting ink coated side as shown in the cross-section of thechromagram in FIG. 10. The three-dimensional like magnetically formednumber 100 can be seen through the polyester substrate 82 in demetalizedboxes 87 as well as rainbow-colored holographic images of the number 100can be seen in holographic boxes 83.

Enhanced chromagrams can also be fabricated by an alternative method. Incontrast to the chromagrams in FIG. 9 and 10, the color-shifting coating88 in this method can be applied to the non-embossed side on thesubstrate 81 as shown in FIGS. 11 and 12 and placed into the field toalign magnetic particles to form the 100 pattern 89. After curing of theink 8 with aligned magnetic pigment, the structure shown in FIG. 11 wasturned over and laminated to the paper 82 with adhesive 90 as shown inFIG. 12. The three-dimensional like magnetically formed pattern 89 ofthe number 100 can be seen through the polyester substrate 81 indemetalized windows 87 and the rainbow-colored holographic images of thenumber 100 surrounded by the frame in the area 83.

The chromagrams in FIGS. 6 through 12 described samples whenmagnetically generated prints were placed either outside or inside of ademetalized holographic image. In some cases demetalized holographicembossing may overlap the magnetically formed image to enhance itsappearance. Examples of such chromagrams are shown in several figuresbelow. Polyester substrate 131 in FIG. 13 has an aluminum metalizedembossed frame 132 and metalized embossed contours 133 of the sign 134in the shape of AB. The regions 135, 136, 137, 138 and 139 aredemetalized.

A cross-section of the substrate 1 with demetalized pattern of FIG. 13is shown in FIG. 14. Magnetic ink containing magnetically orientableparticles is separately printed in two areas on the top of the embossedsubstrate. In exemplary embodiments gold to blue color-shifting ink wasapplied in one sample, colored color switching non-color-shifting inkvehicle was applied in another sample, and magnetic diffractive ink wasapplied in another sample. While wet, each of the prints was separatelyoriented in an applied magnetic field and separately cured. The printedsubstrate was flipped over so as to face and receive incident light rayswith its non-embossed side and laminated to the paper 142 with theadhesive 133. Different orientation of magnetic pigment particlescreated color or contrast difference in printed areas as shown in FIG.15. Layer 141 of the ink, in the background areas 135, 138 and 139 arebright gold at a normal angle of observation. The sign AB is blue atthis angle while the frame 132 and contours 133 have rainbow-likecolors. Alignment of the pigment particles and the light rays reflectionare shown in the cross-section of the structure in FIG. 16.

The AB 134 was printed in the margins of the sign's contour lines 133. Amagnetic field applied to the layer 140 of the wet ink providedalignment of the pigment particles as shown in FIG. 14 in apredetermined manner. Layer 141 of the ink in the background areas 135,138 and 139 has different alignment of particles. The particles here arealmost parallel to the substrate.

Observations of the structure in FIGS. 15 and 16 show that the rays 144incident from a distant light source penetrate the transparent polyestersubstrate 131 and are reflected from the magnetic particles 145 of thepigment. The direction of reflection of the light rays depends on twofactors: alignment of the particles dispersed in the cured ink vehicleand the observation angle. At normal angle, as shown in FIG. 16, thelight rays 144, reflected from the particles in the background layer141, shine in the direction 146 to the observer 147. The observer sees agold background layer 141 and sees this in areas 135, 138 and 139 inFIG. 15. The particles in the layer 140 of the sign AB are tilted at alarger angle with respect to the viewer than the particles in thebackground layer 141. At this particular angle of observation, thereflectance maximum of the particles shifts to the region of shorterwavelengths and the light of short wavelengths shines in the direction148. The observer sees the sign AB as dark blue. The frame 132 and thecontours 133 are rainbow-colored.

The tilt of the sample from the observer changes the observation angleof the particles. Particles in the layer 140, that is, the sign AB, areat a normal angle with respect to the observer while the particles inthe background layer 141 are tilted as shown in FIG. 17. Layer 143 is anadhesive layer.

Now the particles in the layer 140 reflect yellow light rays in thedirection 146 and the observer sees the sign AB as gold in color.Background particles in layer 141 reflect blue light in the direction148 and the observer sees dark blue background areas surrounding thesign AB as shown in FIG. 18. The frame 132 and the contours 133 maintainthe same rainbow colors.

In addition to the embodiments described above, an alternate structureis shown in FIG. 19 a, which combines a magnetically formed image and ahologram, that has incredible appeal. The structure includes atransparent substrate with embossed holographic pattern. Regions arecoated with metal and other regions are absent metal or demetalized.This is visible through the substrate and both the holographic effectand the magnetically aligned coating effect are viewed.

It has been discovered that the presence of reference points in anoptically illusive image produces a very strong illusion of the depthwithin an image. For example using a magnetically aligned pigment with areference point has significant advantages. The reference point could beanything located in close proximity the printed layer that could be seenby the naked eye and which provides awareness to the viewer of thelocation of the layer. The reference points include printing, writing,dusting or splattering of paint on the top surface of the magneticallyoriented layer. Additionally, the surface of the printed layer could betextured by cutting, scratching, etching, or the like; provided atextured surface on the substrate so that a layer of the ink adheredthereto will have a textured surface; a top coat containing particlesvisible to the naked eye such as flakes, specks, etc. Turning now toFIGS. 19 a and 19 e, an optically illusive image useful as a securitydevice to protect a substrate or contents of a package is shown. Thisimage is printed in a manner similar to the aforementioned images,however a fixed printed image of a bridge serves as a reference pointjuxtaposed with an optically illusive kinematic image of water whichappears to move relative to the bridge. The bridge and other elements ofthis figure are shown as fixed images that do not have opticallyillusive properties. In contrast, the water 193 underneath the bridgeappears to move as the image is tilted or the direction of incidentlight upon the water 193 is varied. The contrast between a fixed portionof the image and a visually perceived moving portion of the imageenhances the illusion of movement of the water 193. The bridge 191 andsurrounding other fixed elements in the figure provide a frame ofreference against which the water 193 under the bridge changes providingthe appearance of movement. The bridge 191 is a partially demetalizedhologram; the landscape 194 around the water can either be a transparenthologram coated with a high index transparent material or a selectivelydemetalized hologram. The sky can be a selectively demetalized hologramas well. The waves in the water 193 are printed with magnetic pigmentaligned in an applied field along magnetic lines. Exemplary magneticsystems for alignment of particles to form the wave pattern are shown inFIGS. 19 b through 19 d, wherein the image is seen in the substrateabove the magnets.

Regions 194 in FIG. 19 e are metalized. Region 195 is transparent.Region 196 is a transparent hologram coated with high index material,whereby optically variable ink can be seen through this area. Regions194 are metalized. The water shown in FIG. 19 f is added to the image inFIG. 19 e by printing magnetic ink in the field shown absent water underthe bridge in FIG. 19 e and applying on of the magnetic field generatedfrom one of the aforementioned magnetic systems. Optically variable inkis also applied to the sky region of the image and is not magneticallyoriented by a magnetic field; notwithstanding this region has a distinctcolor shift. It is interesting to note that the same optically variableink applied to the water region and the sky region have very differentvisual effects. The water has an appearance of moving waves having akinematic effect as the flakes are magnetically oriented and the sky hasa color-shifting appearance with no kinematic effects; both the sky andwater regions are preferably printed simultaneously.

The bridge 191 in FIG. 19 a is an image of an object capable of castinga shadow. When such an object is printed whereby the print is a fixedprint and when magnetically aligned optically illusive pigment isapplied near, under or beside the fixed image of the object, theillusive magnetically aligned pigment is perceived to be highlykinematic juxtaposed to the fixed print of the object.

The inventors of this invention have found that the presence of ahologram on the top or around a magnetically formed image generates athree-dimensionality to the image. In accordance with this invention thediffractive pattern serves as a frame of reference; that is, referencepoints relating to where things are with respect to one another.Illusive or virtual depth of the disclosed optical device depends onseveral constituent factors. The factors for the magnetically formedpattern include magnetic pigment color and brightness, thickness of thelayer of the ink, sharpness of magnetically generated pattern, contrastratio between the background and the magnetically generated pattern.Factors for the hologram include level of transmittance of the coatedlayer.

A diffractive pattern can be embossed in such a manner that it would beinvisible at normal angle of observation allowing viewing of a magneticprint and become gradually highly visible at rotation of the print from0 .degree. to 90 .degree. around the axis perpendicular to the surfaceof the diffractive embossing. A transparent blazed-patterned diffractivegrating laminated to a magnetically formed image, is very good for thispurpose.

Another significant advantage of using a transparent hologram is anincreased capacity of information that can be placed into the opticaldevice. A magnetically aligned image may form a pattern that would carrya particular amount of information or text and the transparent hologramlaminated on the top of magnetic print would carry another amount ofinformation or additional text. Both of these difference sources ofinformation could overlap one another providing multiple informationsources of different information covering a same viewing region,essentially increasing the information storing capacity of a sameviewing region.

Various other embodiments may be envisaged without departing from thespirit and scope of the invention. For example, the light transmissivesubstrate can be coated with a high index layer, and coated withmagnetically aligned pigment is any desired pattern and subsequentlystamped with an embossed grating.

The high index layer can used in place of demetalized or patternedaluminum layer as noted above. The high index layer, also referred to asa high refractive (HRI) layer, is a coating composed of a highrefractive index (HRI) material having an index of refraction at least1.65. Suitable examples of such materials are known in the art andinclude TiO₂ and ZnS. The reason for the use of the HRI layer is toprovide reflectance from the embossed pattern. Without the HRI layer,the embossed layer is very similar in refractive index to a laminatingpolymer and thus its diffractive optical effects would essentiallydisappear if a layer of a material having a differing refractive indexdifference is not provided. The HRI is a substitute for the aluminumused to provide the reflectance.

There are two types of demetallized Al coatings used on holograms. Inthe one instance, the coating is completely removed over an extendedarea, e.g. a “window”, to permit viewing of a feature or backgroundbehind the coating. In another embodiment, the coating is a so-called“partial demetallization” where the coating is made to looksemitransparent by demetallizing in a very fine dot screen pattern likenewspaper halftone printing, so that both the reflected holographicpattern and the background can be seen together like looking through awindow screen with very fine weave. A HRI coating used for the lattereffect, by enhancing the reflectance of the holographic surface andmaking it visible even when laminated to a medium of the same refractiveindex as the underlying embossment by increasing the refractive indexdifference of the surface. HRI coatings have several advantages. Theyare continuous and so do not show a “dot screen” pattern or moire effectin combination with other printed patterns or overlays, and more durableand corrosion resistant than the very thin Al coatings needed forpartial demetallization. The degree of reflectance and the color ofreflectance can be varied within certain limits by varying the HRIthickness, using the changes in interference color produced by the HRIlayer itself. However, they are thicker and more expensive to apply thana simple Al layer.

In addition to the reflected/transmitted color control by interferencecolors in a transparent HRI layer, the HRI layer may have intentionalabsorption by using for example a suboxide of for example titanium orother metal, or even color centers or cermet materials such as SiO2/Crcermet.

There are a number of well known ways to produce a patterned HRI layer.The HRI coating may be deposited by using a contact mask to delineatethe regions where the HRI coating is windowed. A printed-on patternedlayer of soluble polymer may be applied to the device, over which theHRI is subsequently deposited. The polymer may then be removed using a“lift-off” process to open windows in HRI layer. HRI layers may bedeposited by well known methods including direct or reactive sputtercoating, vacuum evaporation, reactive plasma deposition of, for example,organometallic compounds, or sol-gel solution coating methods.

According to one embodiment, FIG. 21 a schematically shows a chromagram200 similar to one shown in FIGS. 1-4 a, wherein the demetallizedaluminum layer having a window in region 7 is substituted with awindowed HRI coating 230. A diffractive grating 210 embossed directly onthe surface of a substrate 220 or upon a coating adjacent to thesubstrate 220 is partially coated with the HRI coating 230, so as toform an embossed region 233, wherein the HRI material is coated directlyonto the diffractive grating 210, and a region 234, embossed and notcovered with the HRI material, whereby forming a window 240 in the HRIcoating above the region 234. It is understood that such a window is aregion having an absence of HRI material and not a window of a lighttransmissive material like glass. In a preferred embodiment the HRIcoating is coated in a pattern forming a plurality of windows. The sideof the substrate opposite to the embossed side is coated with a colorshifting coating 250, which may be a coating containing pigmentparticles magnetically aligned, as described above, or a layered colorshifting thin film structure, or a color shifting ink. The layered thinfilm structure can be a foil made of thin layers: an absorber layer, areflector layer, and a dielectric layer, adhesively bonded to thesubstrate. Alternatively, the thin layers can be deposited onto thesubstrate using techniques known in the art. In another embodiment, thecoating 250 is made of a regular ink printed onto the substrate 220.

In operation, when the chromagram 200 is irradiated with light, the HRIcoating 230 enhances reflectance from the embossed surface 210, and thecolor shifting coating 250 is visible through the transparent substrate220 and window 240 in the HRI coating 230, so that a color shiftingimage formed by the region 234 serves as a reference to a diffractiveimage formed by the region 233.

According to one embodiment, FIG. 21 b schematically shows a chromagram201 similar to one shown in FIGS. 4 b and 5, wherein an HRI layer 231substitutes a metal layer between a color shifting coating 251 and anembossed surface 211 of a substrate 221 or upon a coating adjacent tothe substrate 221. The HRI coating 231 is windowed or segmented so thatthe diffractive grating 211 has at least one region 235 coated with theHRI material, and at least one region 236 absent any HRI material thusforming a window in the HRI coating similar to the window 2 shown inFIG. 4 b.

In one embodiment, the color shifting coating 251 is a Fabry-Perotstructure consisting of an absorber layer, a reflector layer and aspacer layer therebetween, wherein the absorber layer is the closest tothe HRI coating 231, for example coated on or adhesively bonded to theHRI coating 231. When the chromagram 201 is irradiated with light,looking in direction marked by an arrow 242 through the transparentsubstrate 221, one can see a color shifting image formed by lightreflected from the color shifting coating 251, visible through thewindow in the region 236 absent the HRI material. A region 235 havingthe HRI coating underlying the diffractive pattern 211 provides aholographic image visible through transparent substrate 221, wherein thecolor shifting image provides a reference to the holographic image.

In the instance when the coating 251 is made of color shifting ink, thecolor shifting effect is visible not only in direction 242 as describedabove, but also on the opposite side when the chromagram 201 is viewedin direction 241. If the HRI coating 231 is coated conformally upon theembossing 211, the optical effect observed in the region 235 depends onconcentration of color shifting particles in the ink vehicle. In theinstance when the pigment particles are transparent or theirconcentration is low, not higher than about 5% by volume or less thanabout 75% by surface area coverage, the HRI-coated diffractive surfacein the region 235 is visible through such a coating thus providing acolor shifting holographic image adjacent to a color-shifting imagewithout a holographic component in the region 236. However, if theconcentration of particles is high enough, they mask or hide theembossing 211 so that a holographic effect is not seen on the top of thechromagram 201; the pigment particles act rather like a random dotscreen as in the case of partial demetallization discussed above. Thevisibility through the pigment coating depends on coating thickness, onthe reflectance and color of the pigment compared to the brightness,color and contrast of the background.

According to one embodiment, FIG. 21 c schematically shows a chromagram202 wherein a color shifting coating 252 is interposed between adiffractive grating 212 and an HRI coating 232. The diffractive grating212 is embossed directly on the surface of a substrate 222 or upon acoating adjacent to the substrate 222. The color shifting layer 252 is alayered thin film structure conforming to the relief of the diffractivegrating 212, for example a Fabry-Perot structure having a reflectivelayer conformally coated on the diffractive grating 212, in turnconformally coated with a spacer dielectric layer, and then with anabsorber layer. The HRI layer 232 conformally coated on the absorberlayer is windowed or segmented so that the diffractive grating 212 hasat least one region 237 coated with the HRI material, and at least oneregion 238 absent any HRI material thus forming a window in the HRIcoating 232.

When the chromagram 202 is irradiated with light and viewed in directionof arrow 244, the color shifting coating 252 is visible in the window inthe region 238, providing a color shifting image in proximity to aholographic image formed by the HRI coating 232 in the region 237. Thecolor shifting image provides a reference to the holographic image,which can be used as a security feature or for aesthetic appeal.

Alternatively, coating layers 250, 251, and 252 are not color shiftingbut colored non-shifting coating, for example images printed withregular ink and visible in the windows of the respective HRI layers.

1. A security article comprising: a substrate; a diffractive gratingdirectly on the surface of the substrate or upon a coating adjacent tothe substrate, having a first region and a second region adjacent to thefirst region; wherein the first region is coated with a high refractiveindex (HRI) coating of a light reflecting HRI material having an indexof refraction at least 1.65 and where the second region is absent theHRI material thereby forming a window above the second region of thesubstrate; a colored or color shifting coating supported by thesubstrate and visible through the window; whereby, when the article isirradiated with light, an image formed by light reflected from thecolored or color shifting coating in the window provides a reference toa holographic image formed by light reflected from the HRI coating.
 2. Asecurity article as defined in claim 1, wherein the HRI coating isdisposed directly on the diffractive grating.
 3. A security article asdefined in claim 2, wherein the colored or color shifting coating is onthe HRI coating.
 4. A security article as defined in claim 3, whereinthe HRI coating conforms to the shape of the diffractive grating and thecolored or color shifting coating comprises an ink vehicle with aplurality of pigment particles dispersed therein, wherein the pigmentparticles are transparent or the concentration of the pigment particlesis less than about 75 percent by area.
 5. A security article as definedin claim 2, wherein the colored or color shifting coating on the side ofthe substrate opposite to the diffractive pattern.
 6. A security articleas defined in claim 1, wherein the colored or color shifting coating isinterposed between the diffractive grating and the HRI coating.
 7. Asecurity article as defined in claim 6, wherein the colored or colorshifting coating and the HRI coating conform to the shape of thediffractive grating.
 8. A security article as defined in claim 1,wherein the colored or color shifting coating is one selected from thegroup of: a color shifting thin film coating, a color shifting ink, aregular ink, a coating having pigment particles aligned in apredetermined manner dispersed therein.
 9. A security article as definedin claim 1, wherein the diffractive grating is one selected from thegroup of: an embossed pattern, a blazed-patterned diffractive grating.10. A security article as defined in claim 1, wherein the diffractivegrating is a segmented diffraction grating, wherein the surface of thesubstrate or the coating adjacent to the substrate has a region void ofdiffractive grating adjacent to the diffractive grating.